One way audio loss 3300 connected via IP trunks to SX200 ICP MX

[Yellowhead]

Hello,
Installed a 3300 at company location "A". Connected to SX200 ICP at company location "B" via IP trunks on company WAN. (WAN is radio between sites)  Had an intermittent problem from day one on site to site extension calls. Three second delay in set up of audio on the 3300 side. IT techs had me use VLAN 110 at site A and VLAN 10 at site B. After much back and forth IT techs had me put both Mitel systems on VLAN 10. They did some other upgrades to routers and firewalls.
Now trouble has changed. It is still intermittent. Calls set up fine (no initial delay) but audio from 3300 side drops after several seconds. Immediate subsequent calls between same extensions have no audio from 3300 side. After waiting for some time it seems to reset to: call is fine then audio drops after several seconds, subsequent calls no audio. I did find one phone at site B I could call and not have problem happen at all. I went to site B today to see if that set was programmed differently. It had L2 priority default set to 6 and no settings for L2 Voice or L2 Signal as I usually put those to 6. I thought I may have found a solution. But after changing another set to these settings I discovered I could not get the trouble to reoccur on ANY test calls this morning. It's hard to fix something that ain't broke. Asked them to call me back when it starts doing it again. Calls started failing again a couple hours later. Any help would be appreciated. Also a link to a resource that may explain to me how the Mitels set up and release these calls would help. I really don't know how calls are handled by the Mitels in this environment. Thanks folks.

[VinceWhirlwind]

Does the path between sites traverse a firewall?

[x-man]

One of the issues with 3300 at least is that they treat IP trunks as internal calls (true for external trunks anyway) so you have to be careful when configuring internal settings because they affect what to all intents is external.

The 3300 only monitors the call once the SIP negotiation is complete and all communication between endpoints is between those endpoints in RTP ( https://www.voip-info.org/wiki/view/RTP).

[Yellowhead]

Thanks for the replies. There are firewalls.  I'm guessing when the 3300 releases control of the call to the network that is when the audio cuts out. Not sure why it is intermittent and why immediate subsequent calls get no audio right away. Spoke to a Bell Canada tech who wants me to try a conference call and see if call audio drops. He says the mitels don't relinquish control of a conference call. Also there are some routing options in system options I want to check. Love the VOIP. Give me E & M any day.

[Yellowhead]

Firewalls are WatchGuard T50-W Firebox. As expected call audio is restored when adding a caller in conference. Route optimization options were set to 3 attempts, 10 seconds , no network id, 2 trailing digits. I think I'm on the wrong track with the system options.

[Yellowhead]

Now I'm being told there are no firewalls in between sites. Same network for all intents and purposes.

[VinceWhirlwind]

OK, if there is no firewall in the picture, maybe the radio needs to be looked at.
What kind of radio? I know I've had trouble with cellular interfaces not passing some kinds of traffic, which I've had to fix by logging into the radio interface itself and adjusting the defaults.
You're going to have to do packet traces to figure out where the traffic is going missing.

[Yellowhead]

Anyone know why a 5312 set at Site B would behave any differently? I cannot reproduce the audio loss when placing calls into one 5312 set that is set up like all the rest of the IP phones that happen to be 5330s.

[Yellowhead]

So someone told me it sounded like a gateway issue. Who ever that was thank you. I didn't program gateways into the phones as they were on the same network. When I did program the gateways into the sets the one way audio disappeared. Thanks to all.